Chemical Vapor Deposition (CVD) is the process of depositing a solid material from a gaseous phase onto a substrate by means of a chemical reaction. The deposition reaction involved is generally thermal decomposition, chemical oxidation, or chemical reduction.
The apparatus of this invention is a CVD apparatus primarily useful for coating semiconductor wafers in the manufacture of solid state electronic devices and energy conversion devices.
With the continuing reduction in integrated circuit component size and multiplication in the number of components per chip, particle contamination and resulting device defects have become an increasingly serious problem. Vertical and horizontal tube reactors use wafer boat assemblies which can be loaded by robot in a dust-free environment, reducing environmental particle contamination. However, these reactors produce contaminating particles in the coating process.
The CVD deposition process, itself, is a major source of particles which can contaminate wafer surfaces, create defects, and lower production yields of advanced devices. In reactions exemplified by the chemical vapor deposition of silicon nitride, for example, dichlorosilane and ammonia are heated to form a reactive mixture which coats the wafer surface with silicon nitride. Dichlorosilane and ammonia begin to react and form particles as soon as the mixed gases reach a threshold reaction temperature, and particulate contamination is unavoidable with the reactors available prior to this invention. In pyrolytic reactions such as the deposition of polysilicon from gaseous silanes, for example, particulate formation and contamination of wafer surfaces has also proven to be a major problem. Overheating the reactants away from the wafer surface and the presence of zones of recirculation or stagnation in the reaction vessel both contribute to particle formation. Formation of particles which can foul the semiconductor products is also a problem in other types of low pressure reactions.
The improved CVD apparatus and process of this invention greatly reduce particle formation and particulate contamination of wafer surfaces.